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Once you’ve found your ideal position on an existing bike or through a new fit, you can mimic that position on a new frame or cockpit using a tape measure and a calculator. Translate the fit accurately and your new ride will be comfortable immediately.

A fitting will tell you the locations of the contact points on a bike–saddle, pedals and aerobar–using stack and reach dimensions to describe the location of the elbow pads. Between your body and your bike frame are aerobars, a stem and headset spacers, and changing the shape and size of these pieces adjusts the fit of your bicycle. In order to connect fit geometry to frame geometry, all these intermediate pieces need to be accounted for.

At the conclusion of a fitting, you should be provided with the coordinates of your contact points that determine your position (or measure an existing bike with the instructions in red). Pay the closest attention to arm pad stack and arm pad reach:

– Pad reach: the horizontal distance from the back of the arm pad to the bottom bracket

Note: These numbers are different from frame stack and reach. If you already have a bike that fits you well, you can measure pad stack and reach from the bicycle. Keep in mind that the saddle position is important when setting up your bike to fit correctly, but not very important when considering if a bike will fit because most modern triathlon seat posts have a wide range of adjustability.

If you are the owner (or the prospective owner) of a triathlon bike with an integrated front end such as the Cervélo P5, the Trek Speed Concept or the BMC Time Machine, check with each manufacturer (or look on the company’s website) to see how your fit requirements align with their bikes.

Translating Pad Position

Aerobars: Many of them are shaped and sized uniquely and have different adjustability ranges. The stack height of the arm rest pads above the basebar center and the arm pad setback behind the basebar center impact a bike’s fit options. The arm pad and extension width are also things to consider when picking an aerobar. Many manufacturers publish their aerobar pad stack and pad setback ranges; the data of a few of the popular bars are listed in the chart below.

Stems: As a general rule, it is desirable to buy a tri bike that fits well with a stem that is 80–110 millimeters long. Aside from adjusting your aerobars, changing the stem can really change the way a bike fits, handles and looks. Stems that are too long or short will make the bike handle poorly. It is also desirable to buy a bike that fits well with a stem that has an angle between –17 degrees and –6 degrees, but you can stray a bit if needed. Stems are available in a wide range of angles and can be installed pointing up or downward so a –6 degree stem can be flipped over to become a +6 degree stem.

Headset spacers: They are rings that sit above your headset cap and below the stem, propping the aerobar higher. You can adjust the height of your aerobars by adding or removing spacers below the stem. It is generally considered a safety hazard to use more than 30mm or 40mm of spacers with today’s carbon forks.